Extreme Weather and the Great Barrier Reef The summer of 2010-11 brought unprecedented weather conditions to Queensland. Cyclone Yasi was one of the most powerful cyclones to have affected the Great Barrier Reef since records commenced, while South East Queensland experienced intense rainfall, up to 400 per cent higher than normal. These extreme weather events damaged coral reefs and seagrass beds, leading to additional pressures on important species such as dugong and green turtle. They also had implications for the industries and communities that depend on the Reef, including direct damage to infrastructure and impacts to natural resources. Coral reefs have a natural ability to recover from extreme weather impacts, enabling the Reef to bounce back from these events. While the Great Barrier Reef is expected to cope with the impacts of climate change better than most coral reefs around the world, the spate of severe floods and intensity of recent cyclones will test its resilience. The Great Barrier Reef Marine Park Authority implemented the Extreme Weather Response Program to better understand the impacts of extreme weather on the Great Barrier Reef and help Reef industries and communities prepare for future extreme weather events. Climate scientists predict increased frequency of extreme weather events such as flooding rains and intense cyclones as a result of climate change. The effects of recent extreme weather events highlight the need for effective management and active stewardship. Insights from the Extreme Weather Response Program are being used to guide the focus of management into the future and to help build the resilience of the Reef and its industries and regional communities to climate change. What was so “extreme” about the summer of 2010-11? Summer is always a period of heightened The summer of 2010-11 risk for the Great Barrier Reef. Warmer conditions bring the threat of high sea temperatures that can cause coral bleaching • Cyclone Yasi was the first category five cyclone to cross the coast since 1918. and wet seasons with strong monsoonal conditions can result in large flood plumes • South East Queensland experienced and damaging cyclones. rainfall 300-400 per cent higher than average. While regional climate processes such as El Niño Southern Oscillation (ENSO) cause seasonal weather patterns to swing between clear/dry (El Niño) and cloudy/wet prevalence of coral bleaching in El Niño (La Niña), global climate change is altering summers and more damage from floods and the underlying conditions. Already, we are cyclones during La Niña years. seeing patterns consistent with predicted The summer of 2010-11 featured an effects of climate change: an increased unusually strong La Niña event. It brought exceptional weather across Australia, resulting in the second wettest summer on record. In South East Queensland, the summer saw intense rain and devastating floods. North Queensland experienced tropical cyclone Yasi’s very destructive winds and a powerful storm surge. In combination, the summer of 2010-11 had brought conditions unprecedented in the history of the Great Barrier Reef Marine Park. This was not the only wet and windy summer for the Great Barrier Reef. Three Flooding in the Great Barrier Reef catchment during of the last four summers have all had above summer 2010-11 created persistent flood plumes average rainfall in eastern Queensland from the Fitzroy, Burnett and Mary Rivers. associated with La Niña conditions. About this report The Great Barrier Reef Extreme Weather Program assisted us to understand what extreme cyclones and floods mean for the Reef and the people who depend on it. It also helped target efforts to support recovery of damaged areas and build the resilience of the Reef over the longer term. This report presents key findings from the Program and profiles management and stewardship efforts that have been put in place to help the Reef cope with the after-effects of extreme weather. It also provides an overview of extreme weather in the context of climate change and the long-term outlook for the Reef and its management. 2 EXTREME WEATHER AND THE GREAT BARRIER REEF The cumulative effects of these wet seasons have meant that some sensitive species (such as corals, seagrasses, green turtle and dugong) were particularly vulnerable to the extreme weather conditions that occurred in the summer of 2010-11. Why is extreme weather a problem for coral reefs? Cyclonic winds and floodwaters can have severe impacts on coral reef ecosystems. Floodwaters entering the Great Barrier Reef can cause stress to inshore ecosystems Large, intense cyclones, such as cyclone Yasi, can through reduced salinity, increased have impacts that affect large areas and last for decades, if not centuries. turbidity and elevated concentrations of nutrients and agricultural chemicals. Corals and seagrasses provide essential Prolonged exposure can lead to death in habitat and food for many other species such some species, especially sessile (attached) as fish, turtles and dugong; their loss can organisms such as corals and seagrasses. have flow-on effects through the system. Cyclone Yasi crossed the Great Barrier Reef near Dunk Island, exposing the coast and adjacent areas of the Great Barrier Reef Marine Park to wind gusts up to 285 km/h. Extensive flooding resulted in persistent floodplumes in the central and southern Great Barrier Reef. WHAT Was so “EXTREME” ABOUT THE SUMMER OF 2010-11? 3 Six severe cyclones have impacted the Great Barrier Reef since 2005. The greater frequency of extreme weather events will reduce the time for reefs to recover between disturbances. Some species, especially various types Tropical cyclones affect coral reefs of algae and crown-of-thorns starfish, can in different ways. Cyclones cause actually benefit from the increased input exceptionally strong winds which of materials (e.g. nutrients), leading to generate powerful waves that crash onto imbalances in the system. shallow reef areas and create damaging turbulence in deeper areas. Flood plumes, caused by the intense rainfall that often accompanies cyclones, can expose large areas to stressful changes in water quality. Particularly intense and large cyclones, such as cyclone Yasi, can also cause destructive currents as huge amounts of water are driven by sustained winds and waves. Through the direct forces of waves and currents, and the impacts of sand and rubble tossed around by underwater turbulence, Cyclones cause strong winds that generate powerful cyclones can cause extensive damage to waves, damaging turbulence and destructive currents. They can also cause intense rainfall and flooding. corals and the underlying reef structure. 4 EXTREME WEATHER AND THE GREAT BARRIER REEF Cyclones can cause severe damage to coral and the underlying reef structure through the direct forces of waves and currents, and the impacts of sand and rubble tossed around by underwater turbulence. At reefs exposed to the full force of a cyclone further from the centre of intense cyclones, there can be near-complete destruction damage is generally less severe. Patches of of the coral community and associated reef may still be denuded by the cyclone’s species, leaving a barren and pulverised reef force, but these are usually outnumbered by substrate. For weaker cyclones or at reefs the many patches of surviving coral. At the worst affected sites (pictured right) the impact of waves and wave-borne debris removed almost all traces of sessile (attached) marine life down to at least 15 m depth. However, damage was patchy and areas of healthy reef (pictured left) were observed even within the region exposed to very destructive winds. WHAT Was so “EXTREME” ABOUT THE SUMMER OF 2010-11? 5 The Cardwell foreshore was significantly damaged by Yasi’s very destructive winds and powerful storm surge. Image © Dieter Tracey. Cyclones can also damage seagrasses Cyclones and floods in historical context and other coastal habitats such as The Great Barrier Reef ecosystem mangroves and wetlands. Seagrasses has evolved under a natural regime of in the intertidal zone can be ripped up cyclones and floods, so in many ways by large waves, while deeper seagrass severe weather is ‘normal’. Between 1995 meadows can be scoured by strong and 2009 approximately 34 per cent of currents. Mangroves and wetlands can all coral mortality recorded in long-term suffer the effects of fierce winds and monitoring1 of the Great Barrier Reef is unusual or prolonged inundation. attributable to storm damage. 130 000 120 000 110 000 100 000 90 000 80 000 70 000 60 000 50 000 40 000 30 000 Fertiliser applied (tonnes) 20 000 10 000 0 1975 1935 1940 1955 1960 1970 1915 1920 1930 1950 1990 1995 2005 1910 1985 1945 1965 1925 1980 2000 Total Nitrogen Total Phosphorous Sediments carried into the Great Barrier Reef by There has been a large increase in the amount of floodwaters can settle out and smother corals and fertilisers used in Great Barrier Reef catchments over other animals and plants attached to the seabed. the last century. Elevated levels of nutritents and Image © Steve Spring | Marine Photobank. sediments entering the Great Barrier Reef ecosystem are reducing its resilience. 1 Australian Institute of Marine Science Long Term Monitoring Program 6 EXTREME WEATHER AND THE GREAT BARRIER REEF Seagrasses provide important habitat and food for other species. Recent floods and cyclones have added to the cumulative impacts of multiple, harsh wet seasons, reducing the resilience of seagrass. Image © Dieter Tracey. However, recent conditions are causing reefs and seagrass meadows becomes unprecedented challenges for the Great increasingly important. Chronic stresses Barrier Reef. The floodwaters now entering from reduced water quality can hinder the Great Barrier Reef carry chemicals recovery of damaged seabed communities. (nutrients and pesticides) and quantities of Therefore, the combined effect of increased sediments that would not have occurred flooding and more severe storms means prior to European settlement.